1. Technical Field
The present invention relates to an improved method and detector for monitoring electrical strikes along a power transmission distribution system and, more particularly, to a method and detector which will identify the location within the power transmission system where an insulator flashover event has occurred.
2. Description of the Prior Art
Electrical power transmission lines are commonly suspended from grounded metal towers by means of non-conducting insulator assemblies. The insulators are designed to prevent electrical current flowing from the transmission line(s) to the supporting metallic towers. When a current flows between a transmission line and the grounded tower across an insulator, the phenomenon may be a relatively short duration spark (e.g., microseconds) , or a relatively long duration arc (e.g., milliseconds); such phenomenon are referred to in the art as a flashover. Depending upon the length and intensity of the flashover, damage may occur to the insulator. Even if no visible indication of damage is apparent, such as carbon deposits or other discoloration, the insulator may have been weakened by the flashover event such that servicing and/or replacement thereof is desirable. Principal causes of insulator flashovers are transient power surges resulting from, for example, lightning striking the transmission line or the tower.
Traditionally, locating a transmission tower on which insulator flashover occurred has required manual examination of each insulator, or insulator string, positioned on each tower within the system for visual signs of flashover breakdown. In addition to its obvious time-consuming and labor-intensive nature, this approach is inherently unreliable. As noted, a momentary flashover event may result in no obvious visual damage or weakening of an insulator, in which case manual inspection of each tower could fail to identify the location of the flashover event.
The known art contains at least one attempt to provide a mechanical insulator flashover detector. Japanese patent application disclosure S.59-155771, entitled: "Flash Short Circuiting Display Device," describes apparatus designed to facilitate the discovery of cloud-to-ground discharge events which is characterized by a coil that detects a magnetic flux created by a surge current and that induces a corresponding output voltage. The output voltage is compared with a standard voltage for the transmission line and a display signal is provided whenever the output voltage deviates from the standard voltage. Although somewhat more useful than the manual inspection approach, this "threshold type" detector appears to have a significant drawback in that multiple flashover event signals may be generated along a power transmission system for a single transient power surge. A power surge may travel a significant distance within the system before finally being dissipated. Anytime the magnetic field about the transmission line comparatively varies from the stored reference value then a flashover event signal would be given.
Thus, there appears to exist a geniune need in the art for a more precise approach to the identification and locating of an insulator flashover event caused by a transient power surge, such as that experienced when lightning strikes the power transmission system.